Unity IOC container: inject named instances or types

[David Mäder]

Helpful information to include

Product name: NServiceBus

Version:4.7.8

Stacktrace:

Description:

In Unity framework there's this concept of named instances or named types, where it's possible to have more than object of the same type, distinguished by a unique name. How can I inject such a named instance in a message handler? Or is there a way to inject the Unity container itself, in order to access any items from the container directly? I'm glad for any documentation or example, explaining how to get a firmer grip on the Unity container. Many thanks - David

[simon.cropp]

David

Both the registration and resolution of handlers of Handlers in an internal concern of NSB. So you cannot, for example, change how a Handler is registered in the container to use a delegated or named-parameter constructor.

However you can use Unitys callback functionality to take full control of customizing the instance as it is resolved from the container.

So taking this as a base http://docs.particular.net/samples/containers/unity/

and then add this 

static class Program

{

    static void Main()

    {

        #region ContainerConfiguration

        BusConfiguration busConfiguration = new BusConfiguration();

        busConfiguration.EndpointName("Samples.Unity");

        UnityContainer container = new UnityContainer();

        container.AddExtension(new MyExtension());

        container.RegisterInstance(new MyService());

        busConfiguration.UseContainer<UnityBuilder>(c => c.UseExistingContainer(container));

        #endregion

        busConfiguration.UseSerialization<JsonSerializer>();

        busConfiguration.UsePersistence<InMemoryPersistence>();

        busConfiguration.EnableInstallers();

        using (IBus bus = Bus.Create(busConfiguration).Start())

        {

            bus.SendLocal(new MyMessage());

            Console.WriteLine("Press any key to exit");

            Console.ReadKey();

        }

    }

}

internal class MyExtension : UnityContainerExtension

{

    protected override void Initialize()

    {

        var strategy = new CustomFactoryBuildStrategy(Context);

        //note there are a variety of options available through UnityBuildStage

        //you should pick the one that best matches your specific use case

        Context.Strategies.Add(strategy, UnityBuildStage.PreCreation);

    }

}

public class CustomFactoryBuildStrategy : BuilderStrategy

{

    private ExtensionContext baseContext;

    public CustomFactoryBuildStrategy(ExtensionContext baseContext)

    {

        this.baseContext = baseContext;

    }

    public override void PostBuildUp(IBuilderContext context)

    {

        base.PostBuildUp(context);

        //here you can do any kind of reflection or type logic to 

        //control what is injected into the instance

        //eg perhaps check if the instance inherits form IHandleMessages

        

        MyHandler handler = context.Existing as MyHandler;

        

        if (handler != null)

        {

            handler.InjectedProperty = "Foo";

        }

    }

}

Does this allow you to move forward?

[simon.cropp]

And now i just discover it is possible

Take this registration

        UnityContainer container = new UnityContainer();

        container.RegisterInstance<IMyService>("MyService1",new MyService1());

        container.RegisterInstance<IMyService>("MyService2",new MyService2());

        busConfiguration.UseContainer<UnityBuilder>(c => c.UseExistingContainer(container));

and these services

    public class MyService1:IMyService

    {

        static ILog logger = LogManager.GetLogger<MyService1>();

    

        public void WriteHello()

        {

            logger.Info("Hello from MyService1.");

        }

    }

    public class MyService2 : IMyService

    {

        static ILog logger = LogManager.GetLogger<MyService2>();

        public void WriteHello()

        {

            logger.Info("Hello from MyService2.");

        }

    }

    public interface IMyService

    {

        void WriteHello();

    }

you can use an attribute to inject the names instance into your handler as such

    public class MyHandler : IHandleMessages<MyMessage>

    {

        IMyService myService;

        public MyHandler([Dependency("MyService2")]  IMyService myService)

        {

            this.myService = myService;

        }

        public void Handle(MyMessage message)

        {

            myService.WriteHello();

        }

    }

[David Mäder]

Hi Simon, that's exactly the solution to my problem, thanks very much for that! It's great to arrive at the office in the morning, finding my issues resolved over night; for once time-zones are working in my favour :)